Open-hearth fireplaces are extremely popular throughout the country. However, they are extremely inefficient as room heaters. This is primarily because the fire contained within the fireplace requires and draws air from within the adjacent room. As a result the warm air within the room is pulled into the fireplace and exhausted through the chimney. A negative pressure may be produced within the room to draw cold exterior air through any open or poorly insulated areas.
In answer to this problem, fireplaces have been designed with draft provisions leading to the exterior of the room or building. With these devices, the cool exterior air may be drawn into the fireplace to support combustion rather than allowing the fire to draw the air from within the room. The result is that heat from the fireplace is radiated into the air which is retained within the room and the heated air therefore will permeate the room atmosphere and spread to other rooms. In new construction, the outside draft has been provided as a built-in element of standard fireplace shells. A problem remains, however, in how to effectively remodel existing fireplaces to include the advantage of an exterior air draft control.